Clinical studies show that it significantly reduces the risk of migraine attack, and relieves asthma and chronic bronchitis. New research shows that it relieves the symptoms of hay fever and other seasonal allergies without the drowsiness that antihistamine drugs cause. Traditionally used since the Middle Ages for whooping cough and as a mucus-reducing cough remedy. Prefers wet locations. Purple-rose flowers in spring. Ht. 1m/3ft.